Thrombosis is local coagulation or clotting of the blood in the circulatory system; thrombolysis (Greek lusis, loosening) is the dissolution of a blood clot; a thromboembolism is obstruction of a blood vessel by a blood clot that has become dislodged from another site in the circulation; thrombocyte is another name for a platelet, a small disc-shaped cell fragment involved in clotting; thrombocytopenia (Greek penia, poverty), is a deficiency of platelets in the blood.